Steel 12Cr2Ni4A-HR (Hot rolled)
Supply condition
GB 12Cr2Ni4A
Mill supply condition for forging stock and for shops that will do their own annealing and carburizing.
Values for the HR condition
Other 12Cr2Ni4A tempers and conditions
12Cr2Ni4A is listed in 8 conditions; see the grade overview at 12Cr2Ni4A.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest and most machinable state — the condition gears are rough-cut and hobbed in before carburizing. | 450 | 700 | 20 | 240 HB | — |
HRThis page Hot rolled | Mill supply condition for forging stock and for shops that will do their own annealing and carburizing. | 560 | 800 | 16 | 22 HRC | — |
Normalized | Grain-refining pre-treatment for forgings; gives a uniform structure and stable machining stock removal. | 620 | 850 | 17 | 26 HRC | — |
Cold drawn | Choose for close-tolerance small-diameter shafting and pins where machining allowance must be minimal. | 700 | 830 | 12 | 25 HRC | 5.7 % IACS |
Quenched and high-tempered, ~30–35 HRC | Higher tempering (550–650 °C) for shafts and fasteners machined to final size without carburizing, trading strength for toughness and cutability. | 830 | 1,000 | 15 | 32 HRC | — |
QTDefault Quenched and tempered | Standard GB/T 3077 property condition and the core state under a carburized case — pick when full through-strength with high toughness is needed. | 950 | 1,180 | 12 | 39 HRC | — |
Carburized, hardened and low-temperature tempered | The service condition for gears and races: hard wear-resistant case with compressive residual stress over a tough 35–42 HRC core. | 1,000 | 1,250 | 10 | 60 HRC | — |
Aerospace quality, vacuum-remelted / clean-steel bar | Specify for flight-critical gears and bearings where inclusion cleanliness governs bending and contact fatigue life. | 1,000 | 1,230 | 15 | 40 HRC | 5.7 % IACS |
What is 12Cr2Ni4A-HR?
12Cr2Ni4A-HR is 12Cr2Ni4A supplied in the HR condition — mill supply condition for forging stock and for shops that will do their own annealing and carburizing. 12Cr2Ni4A-HR has a yield strength of 560 MPa (81.2 ksi) and a tensile strength of 800 MPa (116 ksi) — stronger than 73% of steel grades. Elongation at break is 16% and the elastic modulus is 210 GPa (30.5 Msi). 12Cr2Ni4A-HR has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,430°C (2,606 °F). QT is the default condition FabDigit quotes; HR is available on request or by drawing note.
Advantages
- Polishes to a fine finish — 75/100, better than 94% of steel grades
Limitations
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
- High embodied carbon — 2.6 kg CO₂/kg, worse than 87% of steel grades
- Difficult to machine — 36/100, worse than 81% of steel grades
- Poor heat conductor — 33 W/m·K (19.1 BTU/hr·ft·°F), worse than 80% of steel grades
- Low electrical conductivity — 5.7 % IACS, worse than 80% of steel grades
12Cr2Ni4A-HR properties
Typical room-temperature values for 12Cr2Ni4A-HR; 10 are specific to this condition. Other listed values are 12Cr2Ni4A reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
12Cr2Ni4A-HR has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,430°C (2,606 °F).
Mechanical16
12Cr2Ni4A-HR has a yield strength of 560 MPa (81.2 ksi) and a tensile strength of 800 MPa (116 ksi) — stronger than 73% of steel grades. Elongation at break is 16% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
12Cr2Ni4A-HR is rated for continuous service to 200°C (392 °F). It conducts heat at 33 W/m·K (19.1 BTU/hr·ft·°F), worse than 80% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
12Cr2Ni4A-HR conducts electricity at 5.7 % IACS, worse than 80% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of 12Cr2Ni4A-HR takes about 36 MJ of energy and emits 2.6 kg of CO₂ — more than 89% of steel grades. Typical recycled content is 25%.
Manufacturability7
12Cr2Ni4A-HR's machinability is fair (36/100, worse than 81% of steel grades); weldability poor (30/100); formability fair (40/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 12Cr2Ni4A-HR
Is 12Cr2Ni4A easy to machine?
Rough all gear teeth in the annealed (≤269 HB) state with coated carbide and generous coolant; after carburizing only grinding, honing or CBN hard-turning is practical.
Can 12Cr2Ni4A be welded?
Weld only before carburizing — preheat 250–350 °C, low-hydrogen or matching Ni-Cr filler, immediate post-weld temper; high hardenability makes the HAZ crack-sensitive.
Can 12Cr2Ni4A be formed, bent or molded?
Hot forge 1150–850 °C then normalize plus isothermal anneal to break up the bainitic/martensitic as-forged structure; cold forming limited to annealed bar.
What surface finishes work on 12Cr2Ni4A?
No anodizing — protect with black oxide, manganese phosphate or oil; copper-plate areas to be masked from carburizing, and shot-peen tooth roots to boost bending fatigue.
12Cr2Ni4A chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CGB/T 3077 12Cr2Ni4A | 0.1 – 0.17 | 0.13 |
| Si | 0.17 – 0.37 | 0.27 |
| Mn | 0.3 – 0.6 | 0.45 |
| Cr | 1.25 – 1.65 | 1.45 |
| Ni | 3.25 – 3.65 | 3.45 |
| Curesidual | ≤ 0.25 | — |
| PA-grade high quality; ≤0.020 for aerospace | ≤ 0.03 | — |
| SA-grade high quality; ≤0.015 for aerospace | ≤ 0.03 | — |
| Fe | balance | — |
12Cr2Ni4A-HR — frequently asked
What is 12Cr2Ni4A-HR used for?
12Cr2Ni4A-HR is typically used for aircraft gears, high-load transmission shafts, planetary pinions and ring gears, spline couplings, precision gearbox pinions and bevel gear sets. In short: aerospace 9310-class gear steel; deep-hardening Ni-Cr case steel; VAR melt available.
What is the yield strength of 12Cr2Ni4A-HR?
12Cr2Ni4A-HR has a typical yield strength of 560 MPa (81.2 ksi) and a tensile strength of 800 MPa (116 ksi) — stronger than 73% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is 12Cr2Ni4A-HR easy to machine?
Not especially — machinability is rated fair (36/100, worse than 81% of steel grades). Rough all gear teeth in the annealed (≤269 HB) state with coated carbide and generous coolant; after carburizing only grinding, honing or CBN hard-turning is practical.
Can 12Cr2Ni4A-HR be welded?
Not readily — weldability is rated poor (30/100). Weld only before carburizing — preheat 250–350 °C, low-hydrogen or matching Ni-Cr filler, immediate post-weld temper; high hardenability makes the HAZ crack-sensitive.
What surface finishes work on 12Cr2Ni4A-HR?
No anodizing — protect with black oxide, manganese phosphate or oil; copper-plate areas to be masked from carburizing, and shot-peen tooth roots to boost bending fatigue.
Can 12Cr2Ni4A-HR be formed, bent or molded?
Hot forge 1150–850 °C then normalize plus isothermal anneal to break up the bainitic/martensitic as-forged structure; cold forming limited to annealed bar.
What is the maximum service temperature of 12Cr2Ni4A-HR?
12Cr2Ni4A-HR is rated for continuous use to about 200°C (392 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 12Cr2Ni4A-QT and 12Cr2Ni4A-A?
QT is the default condition — standard GB/T 3077 property condition and the core state under a carburized case — pick when full through-strength with high toughness is needed. A: softest and most machinable state — the condition gears are rough-cut and hobbed in before carburizing. Yield strength is 950 MPa in QT versus 450 MPa in A.
Sources
- GB/T 3077 Alloy structural steels (2015)
- AMS 6265 — Steel Bars, Forgings and Tubing 3.2Ni-1.2Cr-0.12Mo (9310), VAR — SAE International (2019)
- ASM Handbook Vol. 1: Properties and Selection — Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol. 4: Heat Treating (carburizing of Ni-Cr gear steels) — ASM International (1991)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.